Slavonic

/sləˈvɒnɪk/

noun

1.

a branch of the Indo-European family of languages, usually divided into three subbranches: South Slavonic (including Old Church Slavonic, Serbian, Croatian, Bulgarian, Bosnian, etc), East Slavonic (including Ukrainian, Russian, etc), and West Slavonic (including Polish, Czech, Slovak, etc)

2.

the unrecorded ancient language from which all of these languages developed